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Discussions about batteries often revolve around energy density. What we want is a battery that stores a whole lot of energy in a very tiny volume, preferably in a manner that doesn't involve explosions or fire. At the cutting edge of research, what we get are batteries that are a mix of amazing and amazingly bad.

Modern batteries are, quite frankly, a miracle compared to ye olde lead acid battery. Yet they still contain less energy per unit mass than the equivalent mass of wood. Essentially, we simply don’t pack enough atoms into a small enough volume to compete with hydrocarbons. But, now it seems that graphene—it’s always graphene—might help pack lithium in.

The invisible metal

Although there are many ways to make a lithium-ion battery, the chemistry boils down to the following: lithium is stored in some form at one electrode. The lithium is released as an ion, where it travels to another electrode and reacts. At the same time, the electrons that complete the reaction travel out into the world via one electrode, do some work, and end up at the other electrode, where they complete the reaction.

The key here is that the lithium is usually stored as a light and low-density lithium carbide. Finding materials that increase the density of lithium is one way to increase battery capacity.

Here is where battery research often runs into problems. Lithium is a very light element. Carbon, the other main constituent of a battery, is also a very light element. When viewed through an electron microscope, they look almost identical. That makes it very difficult to examine how lithium builds up at an electrode and makes it hard to see the variations in structures that it forms as it is stored (or how those structures come apart as it is removed).

It is worse than that, though. Electron microscopes usually use quite energetic electrons to create an image. The electrons have more than enough energy to knock carbon and lithium atoms out of the structure being examined. By the time you have created your image, you have destroyed the structure you imaged. Not ideal.

Enter a group of scientists with a transmission electron microscope that has been designed to work with low-energy electrons. The microscope still has sufficient resolution to see single atoms, so structures can be determined. By examining how much energy the electrons lose as they go through the sample, the researchers can also figure out the sample contents. Finally, the time it takes to gather the image is short enough (about one second) that the researchers can observe the build up and decay of structures as the battery is used.

A lithium sandwich

Since transmission electron microscopy requires that electrons pass through the sample, the carbon-lithium layer had to be very thin. The researchers chose to use a ribbon of a graphene double-layer (graphene is a single layer of graphene with the carbon atoms arranged in a honeycomb pattern). A blob of electrolyte-containing lithium ions was placed at one end of the graphene ribbon.

A series of electrodes were placed along the ribbon to measure and set voltages. The voltages were used to drive lithium into the ribbon and allow it to leave again. When lithium accumulates in the ribbon, the resistance drops, allowing a second set of electrodes to detect the presence of lithium.

The researchers don’t say it, but I think they were quite surprised by what happened. The lithium moves quite rapidly in the gap between the two graphene ribbons. On the scale of their graph, lithium appears between the electrodes instantly. From the movie, it looks like it takes about 14s to travel 50 micrometers, which I think is shockingly fast.

The amount of lithium is also pretty surprising. By examining the structure and elemental composition, the researchers found that the lithium was not forming a lithium carbide, as expected. Instead, it was forming multiple layers of crystalline lithium with only the outermost layer binding to the carbon. But the metallic lithium was not in its usual form. Instead, the lithium forms a high-density state that is normally found at low temperature or very high pressure.

Don’t get overexcited

This is quite interesting, and it may even prove useful. But not yet. For one thing, the high-density lithium only forms between two sheets of very nearly perfect graphene, not the sort of graphene that you can buy from a manufacturer. Indeed, near the edges of imperfections, the energy imparted by the electrons in the electron microscope was enough to boil off the lithium metal.

Even if we could get large amounts of high-quality, double-layer graphene sheets, there is no certainty that the lithium will diffuse as deeply as required during a charging cycle. It is pretty easy to imagine the first lithium ion building up in a clump that blocks the rest of the lithium from moving into the sandwich.

It is also not certain that the graphene survives the process for very long. This is one of the main problems with batteries involving metallic lithium: the electrodes destroy themselves over multiple cycles. We’ve no idea if graphene will last any longer than current electrode designs.

That said, the researchers are not presenting this as a battery-ready technology. Rather, it is an excellent example of how an experimental necessity has led to an interesting new set of observations that we will probably learn a lot from. And, if we are lucky, it will eventually help make batteries better.

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Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He Lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com

*Discussions about batteries often revolve around energy density. What we want is a battery that stores a whole lot of energy in a very tiny volume, preferably in a manner that does involve explosions or fire.*

Wanting ever-higher energy densities while being bomb-averse are two desires at dire odds with each other.

Lithium polymer batteries have already reached the same magnitude of energy density as TNT.Think about that, for a second. You basically have several grams of TNT on your face when you're on your phone.Nice talkin' to ya!This message will self-destruct.

If I'm understanding correctly, the 2017 article was reviewing a paper that was about this technique potentially working as a way to increase lithium density. But this article is reviewing a paper that dives in deeper and figures out a lot more about what is going on with the atoms when this technique is used. And it isn't what we expected to find.

Wanting ever-higher energy densities while being bomb-averse are two desires at dire odds with each other.

Lithium polymer batteries have already reached the same magnitude of energy density as TNT.Think about that, for a second. You basically have several grams of TNT on your face when you're on your phone.Nice talkin' to ya!This message will self-destruct.

TNT's destructive power isn't so much in its energy density as it is in the speed with which it can be released. In fact, the difference between TNT and nitroglycerin has a lot to do with structures that reduce the energy density while stabilizing the molecules before they're asked to break down.

LI+ batteries are scary because the exhibit runaway energy release - as they heat up they release their energies faster. Battery technologies that inherently limit the release rate would allow for even higher energy densities with just as much (or more) safety.

If I'm understanding correctly, the 2017 article was reviewing a paper that was about this technique potentially working as a way to increase lithium density. But this article is reviewing a paper that dives in deeper and figures out a lot more about what is going on with the atoms when this technique is used. And it isn't what we expected to find.

Ok.That's what I'm arriving at, too, after re-reading both.Would have been nice to mention that in the article - that this is based on a paper that is a deeper analysis of something that was already hypothesized.

If I'm understanding correctly, the 2017 article was reviewing a paper that was about this technique potentially working as a way to increase lithium density. But this article is reviewing a paper that dives in deeper and figures out a lot more about what is going on with the atoms when this technique is used. And it isn't what we expected to find.

Ok.That's what I'm arriving at, too, after re-reading both.Would have been nice to mention that in the article - that this is based on a paper that is a deeper analysis of something that was already hypothesized.

Also, it appears that the work in the earlier article made electrodes of multiple layers of graphene folding back and forth. It wasn't specifically a twin ribbon with the lithium metal inside. It was a much larger bulk of material.

Wanting ever-higher energy densities while being bomb-averse are two desires at dire odds with each other.

Lithium polymer batteries have already reached the same magnitude of energy density as TNT.Think about that, for a second. You basically have several grams of TNT on your face when you're on your phone.Nice talkin' to ya!This message will self-destruct.

TNT's destructive power isn't so much in its energy density as it is in the speed with which it can be released. In fact, the difference between TNT and nitroglycerin has a lot to do with structures that reduce the energy density while stabilizing the molecules before they're asked to break down.

LI+ batteries are scary because the exhibit runaway energy release - as they heat up they release their energies faster. Battery technologies that inherently limit the release rate would allow for even higher energy densities with just as much (or more) safety.

Well yes. Explosives are useful because of the speed at which the reaction occurs. High energy density just makes them more space-efficient.

But, in the context of consumer electronics:If my face burns off rapidly or is blown off rapidly, I'm not terribly concerned with the distinction.At energy densities that high, the indisputable potential exists for that energy to be released through some mechanism in a fashion that is hazardous to a human. Even normal discharge rates are enough to burn or kill you, if applied the right way, so it's just a given fact. The fact that normal discharge is not the only situation those batteries will exist in is what makes it a problem. See: manufacturing defects, drops, punctures, and shorts, just to name the immediately obvious.

Not intending to be overly alarmist - just being real.Like a lot of modern conveniences, these technologies are GRAS, but need to be respected for the chemistry/physics involved.

Just because I was curious about some other common materials and their energy densities, I googled and found that Wikipedia has a nice chart of several common materials, their energy densities, and their specific energies.Infoporn for anyone who cares: https://en.wikipedia.org/wiki/Energy_density

A funny entry in the second table on the page, which speaks directly to the point you just made, is the energy content of a ham and cheese sandwich, which is more than a typical cell phone battery, but significantly less likely to harm you by thermal death (though I suppose you could try for a very amusing darwin award, if you wanted!).

The oxygen isn't a catalyst. It's a reactant and it's bringing plenty of potential energy to the table as well.

If you're going to be technically critical of a science writer, you might want to make sure your complaint is technically accurate itself.

Thanks for the correction. My intent was not to be critical of the writer but a wish that hydrocarbon fuel be more accurately represented when compared to chemical batteries

Fair enough. But in that case you might want to compare batteries to something like gunpowder that carries its own oxidizer. The best lithium ion batteries are still only half as dense (Mj/L) a the worst gunpowders and a factor of ten lower than the hottest grains. Now, with that said, is a factor of 2-10 a reasonable trade off for controlled release rates and re-usability? I'd say yes. But on the flip side, for applications where we're looking to electrify combustion engines, you have to accept that the air always provides oxygen.

Wanting ever-higher energy densities while being bomb-averse are two desires at dire odds with each other.

Lithium polymer batteries have already reached the same magnitude of energy density as TNT.Think about that, for a second. You basically have several grams of TNT on your face when you're on your phone.Nice talkin' to ya!This message will self-destruct.

TNT's destructive power isn't so much in its energy density as it is in the speed with which it can be released. In fact, the difference between TNT and nitroglycerin has a lot to do with structures that reduce the energy density while stabilizing the molecules before they're asked to break down.

LI+ batteries are scary because the exhibit runaway energy release - as they heat up they release their energies faster. Battery technologies that inherently limit the release rate would allow for even higher energy densities with just as much (or more) safety.

Well yes. Explosives are useful because of the speed at which the reaction occurs. High energy density just makes them more space-efficient.

But, in the context of consumer electronics:If my face burns off rapidly or is blown off rapidly, I'm not terribly concerned with the distinction.At energy densities that high, the indisputable potential exists for that energy to be released through some mechanism in a fashion that is hazardous to a human. Even normal discharge rates are enough to burn or kill you, if applied the right way, so it's just a given fact. The fact that normal discharge is not the only situation those batteries will exist in is what makes it a problem. See: manufacturing defects, drops, punctures, and shorts, just to name the immediately obvious.

Not intending to be overly alarmist - just being real.Like a lot of modern conveniences, these technologies are GRAS, but need to be respected for the chemistry/physics involved.

Just because I was curious about some other common materials and their energy densities, I googled and found that Wikipedia has a nice chart of several common materials, their energy densities, and their specific energies.Infoporn for anyone who cares: https://en.wikipedia.org/wiki/Energy_density

A funny entry in the second table on the page, which speaks directly to the point you just made, is the energy content of a ham and cheese sandwich, which is more than a typical cell phone battery, but significantly less likely to harm you by thermal death (though I suppose you could try for a very amusing darwin award, if you wanted!).

The sandwich is funny.

That said, most battery failures don't happen faster than a second. In that time, if it's next to your face you do have a chance to react. If it's in your pants pocket, however, you might not.

With that said, it's amazing to me how few battery-related incidents there are with consumer electronics even including Samsung's recent troubles (that lead to serious injury or death). We're talking one incident per 10- or even 100-million devices sort of failure rate. Given, as you say, the immense amount of energy in such a small package that's a testament to how durable these devices are.

Wanting ever-higher energy densities while being bomb-averse are two desires at dire odds with each other.

Lithium polymer batteries have already reached the same magnitude of energy density as TNT.Think about that, for a second. You basically have several grams of TNT on your face when you're on your phone.Nice talkin' to ya!This message will self-destruct.

TNT's destructive power isn't so much in its energy density as it is in the speed with which it can be released. In fact, the difference between TNT and nitroglycerin has a lot to do with structures that reduce the energy density while stabilizing the molecules before they're asked to break down.

LI+ batteries are scary because the exhibit runaway energy release - as they heat up they release their energies faster. Battery technologies that inherently limit the release rate would allow for even higher energy densities with just as much (or more) safety.

Well yes. Explosives are useful because of the speed at which the reaction occurs. High energy density just makes them more space-efficient.

But, in the context of consumer electronics:If my face burns off rapidly or is blown off rapidly, I'm not terribly concerned with the distinction.At energy densities that high, the indisputable potential exists for that energy to be released through some mechanism in a fashion that is hazardous to a human. Even normal discharge rates are enough to burn or kill you, if applied the right way, so it's just a given fact. The fact that normal discharge is not the only situation those batteries will exist in is what makes it a problem. See: manufacturing defects, drops, punctures, and shorts, just to name the immediately obvious.

Not intending to be overly alarmist - just being real.Like a lot of modern conveniences, these technologies are GRAS, but need to be respected for the chemistry/physics involved.

Just because I was curious about some other common materials and their energy densities, I googled and found that Wikipedia has a nice chart of several common materials, their energy densities, and their specific energies.Infoporn for anyone who cares: https://en.wikipedia.org/wiki/Energy_density

A funny entry in the second table on the page, which speaks directly to the point you just made, is the energy content of a ham and cheese sandwich, which is more than a typical cell phone battery, but significantly less likely to harm you by thermal death (though I suppose you could try for a very amusing darwin award, if you wanted!).

The sandwich is funny.

That said, most battery failures don't happen faster than a second. In that time, if it's next to your face you do have a chance to react. If it's in your pants pocket, however, you might not.

With that said, it's amazing to me how few battery-related incidents there are with consumer electronics even including Samsung's recent troubles (that lead to serious injury or death). We're talking one incident per 10- or even 100-million devices sort of failure rate. Given, as you say, the immense amount of energy in such a small package that's a testament to how durable these devices are.

Agreed. And a testament to the fact that the engineers designing them did their due diligence.The fact that it was such a shocking and sensational occurrence, for people, in the face of that, just underscores that fact even more.

The oxygen isn't a catalyst. It's a reactant and it's bringing plenty of potential energy to the table as well.

If you're going to be technically critical of a science writer, you might want to make sure your complaint is technically accurate itself.

Thanks for the correction. My intent was not to be critical of the writer but a wish that hydrocarbon fuel be more accurately represented when compared to chemical batteries

The energy is still in the bonds of the long chain hydrocarbons that form wood. There is no battery that has that level of energy density.

And you can bet every oil company on earth has been looking for a way to make hydrocarbon-fueled batteries a reality. Can you imagine the new heights of obscene profitability they'd soar to, if someone figured out a safe and economical way to turn long chain hydrocarbons directly into electricity without the intermediate stages in between (chemical->electrical, rather than chemical->thermal->mechanical->electrical)?

I can only assume, however, that the most likely byproducts of that would be carbon dioxide and water, as that's what happens with perfect combustion of a hydrocarbon, so I kind of hope this never does happen.

Edit: On second thought, maybe I do hope this happens, as skipping the intermediate changes almost certainly means a dramatic increase in efficiency, meaning that the ICE could finally die a long-overdue death without changing our deeply-entrenched fuel distribution infrastructure.

Will searching for Bi lithium sandwich get me thrown out of Starbucks?

Ha.If the apparent intelligence of the baristas at my local starbucks is representative, it'd probably get you a blank stare or an uncomfortable laugh, and then not-quiet-enough comments about "what a nerd that guy is," to the other employees, while they're mixing up your frappuccino.

The oxygen isn't a catalyst. It's a reactant and it's bringing plenty of potential energy to the table as well.

If you're going to be technically critical of a science writer, you might want to make sure your complaint is technically accurate itself.

Thanks for the correction. My intent was not to be critical of the writer but a wish that hydrocarbon fuel be more accurately represented when compared to chemical batteries

The energy is still in the bonds of the long chain hydrocarbons that form wood. There is no battery that has that level of energy density.

I don't have the software to check but I seem to recall that the change in element potential for the oxygen far outweighs the changes for both the hydrogen and carbon. But it's been a long time since I took reaction kinetics. And it's the reaction of oxygen with hydrogen that carries most of the work. So while there's some stored energy in the hydrocarbon bonds, it's the conversion of a double bond between oxygen atoms to two single bonds between H and O that's the majority of the energy release. But again, I'm more than a bit rusty.

The oxygen isn't a catalyst. It's a reactant and it's bringing plenty of potential energy to the table as well.

If you're going to be technically critical of a science writer, you might want to make sure your complaint is technically accurate itself.

Thanks for the correction. My intent was not to be critical of the writer but a wish that hydrocarbon fuel be more accurately represented when compared to chemical batteries

The energy is still in the bonds of the long chain hydrocarbons that form wood. There is no battery that has that level of energy density.

And you can bet every oil company on earth has been looking for a way to make hydrocarbon-fueled batteries a reality. Can you imagine the new heights of obscene profitability they'd soar to, if someone figured out a safe and economical way to turn long chain hydrocarbons directly into electricity without the intermediate stages in between (chemical->electrical, rather than chemical->thermal->mechanical->electrical)?

I can only assume, however, that the most likely byproducts of that would be carbon dioxide and water, as that's what happens with perfect combustion of a hydrocarbon, so I kind of hope this never does happen.

That's basically what a direct methane fuel cell is. Honestly, I'd like to see this technology advance more. If we are still going to bother burning natural gas for power gen, I'd rather see us get more electricity per unit CO2 we emit.

Edit: As per your edit, if we did kill off the ICE that way at least we'd be cutting out a lot of NOx emissions.